Surgical resection is a means of removing sections of highly vascular organs from within the human or animal body, such as the liver or the spleen. When tissue is cut (divided or transected) small blood vessels called arterioles are damaged or ruptured. Initial bleeding is followed by a coagulation cascade where the blood is turned into a clot in an attempt to plug the bleeding point. During an operation, it is desirable for a patient to lose as little blood as possible, so various devices have been developed in an attempt to provide blood free cutting.
For example, the Hemostatix® Thermal Scalpel System (http://www.hemostatix.com) combines a sharp blade with a haemostatic system. The blade is coated with a plastic material and connected to a heating unit which controls the temperature of the blade. The intention is for the heated blade to cauterise the tissue as it is cut.
Other known devices that cut and stop bleeding at the same time do not use a blade. Some devices use radiofrequency (RF) energy to cut and/or coagulate tissue. Other devices, for example the harmonic scalpels, use a rapidly vibrating tip to cut tissue and can provide a degree of coagulation.
The method of cutting using RF energy operates using the principle that as an electric current passes through a tissue matrix (aided by the ionic contents of the cells), the impedance to the flow of electrons across the tissue generates heat. When a pure sine wave is applied to the tissue matrix, enough heat is generated within the cells to vaporise the water content of the tissue. There is thus a huge rise in the internal pressure of the cell, that cannot be controlled by the cell membrane, resulting in the cell rupturing. When this occurs over a wide area it can be seen that tissue has been transected.
Whilst the above principle works elegantly in lean tissue, it is less efficient in fatty tissue because there are fewer ionic constituents to aid the passage of electrons. This means that the energy required to vaporise the contents of the cells is much greater, as the latent heat of vaporisation of fat is much greater than that of water.
RF coagulation operates by applying a less efficient waveform to the tissue, whereby instead of being vaporised, the cell contents are heated to around 65° C. This dries out the tissue by desiccation and also denatures the proteins in the walls of vessels and the collagen that makes up the cell wall. Denaturing the proteins acts as a stimulus to the coagulation cascade, so clotting is enhanced. At the same time the collagen in the wall is denatured and changes from a rod like molecule to a coil, which causes the vessel to contract and reduce in size, giving the clot an anchor point, and a smaller area to plug.
However, RF coagulation is less efficient when fatty tissue is present because the electrical effect is diminished. It can thus be very difficult to seal fatty bleeders. Instead of having clean white margins, the tissue has a blackened, burned appearance. In vascular organs such as the liver there is also the heat sink effect as large volumes of fluid are being perfused through the tissue.
In practice, a RF device may operate using a waveform with a medium crest factor that is midway between a cutting and coagulating output.
The liver is highly vascularised, and for patients with cancers elsewhere in the body, it often becomes a site of secondary cancer. Large tumours or areas affected by numerous smaller tumours have to be resected to stop the cancer spreading throughout the organ, the function of which may already be compromised due to the administration of chemotherapy agents. Due to the concentration of blood vessels in the liver, surgery there is normally associated with high volume blood loss requiring vast quantities of blood to be transfused. Once bleeding starts in the liver, it can be difficult to stop. An argon beam coagulator is one example of a known device that can be used to try to stop the bleeding—this device produces surface coagulation.
WO 2008/044000 discloses surgical resection apparatus adapted to simultaneously cut and seal highly vascularised tissue, such as the liver or spleen. The apparatus comprises a source of microwave radiation that is coupled to a surgical instrument having an antenna associated with a blade for cutting biological tissue, wherein the antenna is arranged to controllably deliver microwave energy from the source to a region where the blade cuts through tissue. The microwave energy can coagulate blood to effectively seal off the blood flow at the cutting region. WO 2008/044000 suggests the use of high microwave frequencies (e.g. 10 GHz or higher), which offer a particular advantage over the use of known lower microwave frequency systems and radiofrequency (RF) systems due to the limited depth of penetration of the energy by radiation and the ability to enable small sharp blade structures to radiate energy efficiently into the tissue to seal off blood flow by being able to produce uniform fields along the length of the blade whilst at the same time being capable of cutting through the tissue to remove sections of diseased or cancerous tissue.
Attention has also been paid to preventing bleeding by advance treatment, i.e. treating the tissue to seal blood vessels before transection. In one known device, two lines of RF energy emitting needles are inserted into the liver tissue to perform in-line sealing. Ideally the RF energy is sufficient to seal the tissue through the full thickness of the liver. The blood supply to the area being transected is thus effectively cut off. When the tissue is subsequently cut through with a blade, there is no bleeding.
Vessels up to 7 mm in diameter can also be sealed using RF energy in a device that can also apply pressure. The vessel is held in a clamping device (e.g. forceps or the like). Pressure exerted on the vessel causes the contents of the vessel walls to be pushed out laterally, whereby the outer wall and inner wall of one side approach the inner and outer wall of the other side. Applying RF energy at this point denatures the collagen of the wall matrix, and it intermingles before being locked in place as the tissue is fully desiccated. When the pressure is released, the newly formed stricture stays in place, meaning that the vessel can be divided, by cutting through the vessel on the efferent side using a sharp blade or the like. New collagen growth takes place through the tangled mass, so the stricture stays in place.
U.S. Pat. No. 6,582,427 discloses an electrosurgery system arranged to generate both RF energy (typically having a frequency of 1 MHz) and microwave energy (typically having a frequency of 2.45 GHz) for operation in a cutting mode or a coagulation mode.